The stronger the forces, the more rigid the matter. Pure Substances are made of the same material throughout and have the same properties throughout. Pure substances cannot be separated into other substances. Some examples are carbon, iron, water, sugar, salt, nitrogen gas, and oxygen gas.
An object which experiences either a change in the magnitude or the direction of the velocity vector can be said to be accelerating. This explains why an object moving in a circle at constant speed can be said to accelerate - the direction of the velocity changes.
